Microsoft SecondLight (MS Research Project)
SecondLight is a new (2008) rear projection-vision surface technology that augments the typical interactions afforded by multi-touch with the ability to project and sense both through and beyond the display.
SecondLight allows users to slide a type of transparent screen on top of the regular Surface display, and see extra info displayed on the screen. For instance, using SecondLight over an image of a car turns it into x-ray specs that show model's wireframe underbelly.
SecondLight uses a switchable diffuser to bring about this effect. When diffuse, the lens is frosted, but applying electricity to the switch causes the lens to go clear. Sensors on Surface will then project specific images to the area SecondLight is occupying. It's a neat trick that adds even more functionality to the Surface, though I'd prefer if they were focusing more on making their table cheap enough for me to afford in the first place.
This technology is a special project specially made for the PixelSense multitouch-tabletop PC but I wish see the possibility of porting this technology to phones and tablets in the future. Microsoft Research has a lot other projects that can really change the way that we use mobile devices like NanoTouch, LucidTouch, SideSight , Lovers Phone and Pocket Touch.